The effect of pressure on the ash formation from the combustion of coals with maceral concentrates at various pressures was analyzed. Two coal samples of different lithotypes and maceral-enriched fractions were prepared from samples of the same bituminous coal seam. It was found that pressure and coal petrographic property influenced char and ash formation under the experimental conditions. The results suggest that the extent of coalescence of included mineral matter of inernite-rich coal sample is more significant than that of the vitrinite-rich coal sample.